U.S. patent application number 11/969330 was filed with the patent office on 2009-07-09 for methods and apparatus for synchronization and detection in wireless communication systems.
This patent application is currently assigned to QUALCOMM INCORPORATED. Invention is credited to Tae Ryun Chang, Je Woo Kim, Chae Kwan Lee, Sameer Nanavati, Jong Hyeon Park, Ju Won Park, Bok Tae Sim.
Application Number | 20090175394 11/969330 |
Document ID | / |
Family ID | 39851402 |
Filed Date | 2009-07-09 |
United States Patent
Application |
20090175394 |
Kind Code |
A1 |
Park; Jong Hyeon ; et
al. |
July 9, 2009 |
METHODS AND APPARATUS FOR SYNCHRONIZATION AND DETECTION IN WIRELESS
COMMUNICATION SYSTEMS
Abstract
A synchronization and detection method in a wireless device may
include performing coarse detection and synchronization with
respect to a received signal. The synchronization and detection
method may also include performing fine detection and
synchronization for acquisition of the received signal. Results of
the coarse detection and synchronization may be used for the fine
detection and synchronization. The synchronization and detection
method may also include performing tracking mode processing when
the acquisition of the received signal has been achieved.
Inventors: |
Park; Jong Hyeon; (San Jose,
CA) ; Sim; Bok Tae; (San Ramon, CA) ; Chang;
Tae Ryun; (Santa Clara, CA) ; Kim; Je Woo;
(Cupertino, CA) ; Park; Ju Won; (San Ramon,
CA) ; Lee; Chae Kwan; (San Jose, CA) ;
Nanavati; Sameer; (Fremont, CA) |
Correspondence
Address: |
QUALCOMM INCORPORATED
5775 MOREHOUSE DR.
SAN DIEGO
CA
92121
US
|
Assignee: |
QUALCOMM INCORPORATED
San Diego
CA
|
Family ID: |
39851402 |
Appl. No.: |
11/969330 |
Filed: |
January 4, 2008 |
Current U.S.
Class: |
375/362 |
Current CPC
Class: |
H04L 27/2659 20130101;
H04L 27/2613 20130101; H04L 27/2665 20130101; H04L 27/2663
20130101; H04L 27/2675 20130101; H04L 5/0048 20130101; H04L 27/266
20130101 |
Class at
Publication: |
375/362 |
International
Class: |
H04L 7/04 20060101
H04L007/04 |
Claims
1. A synchronization and detection method in a wireless device,
comprising: performing coarse detection and synchronization with
respect to a received signal; performing fine detection and
synchronization for acquisition of the received signal, wherein
results of the coarse detection and synchronization are used for
the fine detection and synchronization; and performing tracking
mode processing when the acquisition of the received signal has
been achieved.
2. The method of claim 1, wherein performing the coarse detection
and synchronization comprises: performing coarse signal detection;
performing coarse preamble detection; performing coarse symbol
boundary detection; and performing fractional carrier frequency
offset estimation.
3. The method of claim 1, wherein performing the fine detection and
synchronization comprises: performing fine signal detection;
performing fine preamble detection; and performing fine symbol
boundary detection.
4. The method of claim 1, wherein performing the tracking mode
processing comprises: performing preamble sequence identification;
performing integer carrier frequency offset estimation; performing
segment estimation; performing sampling frequency offset
estimation; and performing physical layer synchronization.
5. The method of claim 1, wherein performing the coarse detection
and synchronization comprises determining auto-correlation of the
received signal using a cyclic prefix property of a preamble.
6. The method of claim 1, wherein performing the fine detection and
synchronization comprises determining auto-correlation of at least
one candidate preamble signal using a conjugate symmetric property
of a preamble.
7. The method of claim 1, wherein performing the fine detection and
synchronization comprises determining cross-correlation of a
preamble with respect to a reference preamble.
8. The method of claim 1, wherein performing the tracking mode
processing comprises determining cross-correlation between the
received signal and possible preamble sequences.
9. The method of claim 1, wherein the coarse detection and
synchronization and the fine detection and synchronization are
performed serially.
10. The method of claim 1, wherein the coarse detection and
synchronization and the fine detection and synchronization are
performed concurrently.
11. The method of claim 1, wherein the wireless device is
configured for use within a wireless communication system that
utilizes orthogonal frequency division multiplexing.
12. The method of claim 1, wherein the wireless device is a user
terminal.
13. A wireless device that performs synchronization and detection
with respect to a received signal, comprising: a coarse detection
and synchronization component that performs coarse detection and
synchronization with respect to a received signal; a fine detection
and synchronization component that performs fine detection and
synchronization for acquisition of the received signal, wherein
results of the coarse detection and synchronization are used for
the fine detection and synchronization; and a tracking mode
processing component that performs tracking mode processing when
the acquisition of the received signal has been achieved.
14. The wireless device of claim 13, wherein the coarse detection
and synchronization component comprises: a coarse signal detection
component that performs coarse signal detection; a coarse preamble
detection component that performs coarse preamble detection; a
coarse symbol boundary detection component that performs coarse
symbol boundary detection; and a coarse fractional carrier
frequency offset estimation component that performs fractional
carrier frequency offset estimation.
15. The wireless device of claim 13, wherein the fine detection and
synchronization component comprises: a fine signal detection
component that performs fine signal detection; a fine preamble
detection component that performs fine preamble detection; and a
fine symbol boundary detection component that performs fine symbol
boundary detection.
16. The wireless device of claim 13, wherein the tracking mode
processing component comprises: a preamble sequence identification
component that performs preamble sequence identification; an
integer carrier frequency offset estimation component that performs
integer carrier frequency offset estimation; a segment estimation
component that performs segment estimation; a sampling frequency
offset estimation component that performs sampling frequency offset
estimation; and a physical layer synchronization component that
performs physical layer synchronization.
17. The wireless device of claim 13, wherein the coarse detection
and synchronization component comprises a cyclic prefix-based
auto-correlation component that determines auto-correlation of the
received signal using a cyclic prefix property of a preamble.
18. The wireless device of claim 13, wherein the fine detection and
synchronization component comprises a conjugate symmetric-based
auto-correlation component that determines auto-correlation of at
least one candidate preamble signal using a conjugate symmetric
property of a preamble.
19. The wireless device of claim 13, wherein the fine detection and
synchronization component comprises a reference cross-correlation
component that determines cross-correlation of a preamble with
respect to a reference preamble.
20. The wireless device of claim 13, wherein the tracking mode
processing component comprises a preamble sequence
cross-correlation component that determines cross-correlation
between the received signal and possible preamble sequences.
21. The wireless device of claim 13, wherein the coarse detection
and synchronization and the fine detection and synchronization are
performed serially.
22. The wireless device of claim 13, wherein the coarse detection
and synchronization and the fine detection and synchronization are
performed concurrently.
23. The wireless device of claim 13, wherein the wireless device is
configured for use within a wireless communication system that
utilizes orthogonal frequency division multiplexing.
24. The wireless device of claim 13, wherein the wireless device is
a user terminal.
25. An apparatus that performs synchronization and detection with
respect to a received signal, comprising: means for performing
coarse detection and synchronization with respect to a received
signal; means for performing fine detection and synchronization for
acquisition of the received signal, wherein results of the coarse
detection and synchronization are used for the fine detection and
synchronization; and means for performing tracking mode processing
when the acquisition of the received signal has been achieved.
26. The apparatus of claim 25, wherein the means for performing the
coarse detection and synchronization comprises: means for
performing coarse signal detection; means for performing coarse
preamble detection; means for performing coarse symbol boundary
detection; and means for performing fractional carrier frequency
offset estimation.
27. The apparatus of claim 25, wherein the means for performing the
fine detection and synchronization comprises: means for performing
fine signal detection; means for performing fine preamble
detection; and means for performing fine symbol boundary
detection.
28. The apparatus of claim 25, wherein the means for performing the
tracking mode processing comprises: means for performing preamble
sequence identification; means for performing integer carrier
frequency offset estimation; means for performing segment
estimation; means for performing sampling frequency offset
estimation; and means for performing physical layer
synchronization.
29. The apparatus of claim 25, wherein the means for performing the
coarse detection and synchronization comprises means for
determining auto-correlation of the received signal using a cyclic
prefix property of a preamble.
30. The apparatus of claim 25, wherein the means for performing the
fine detection and synchronization comprises means for determining
auto-correlation of at least one candidate preamble signal using a
conjugate symmetric property of a preamble.
31. The apparatus of claim 25, wherein the means for performing the
fine detection and synchronization comprises means for determining
cross-correlation of a preamble with respect to a reference
preamble.
32. The apparatus of claim 25, wherein the means for performing the
tracking mode processing comprises means for determining
cross-correlation between the received signal and possible preamble
sequences.
33. The apparatus of claim 25, wherein the coarse detection and
synchronization and the fine detection and synchronization are
performed serially.
34. The apparatus of claim 25, wherein the coarse detection and
synchronization and the fine detection and synchronization are
performed concurrently.
35. The apparatus of claim 25, wherein the apparatus is configured
for use within a wireless communication system that utilizes
orthogonal frequency division multiplexing.
36. The apparatus of claim 25, wherein the apparatus is a user
terminal.
37. A computer-program product for performing synchronization and
detection with respect to a received signal, the computer-program
product comprising a computer readable medium having instructions
thereon, the instructions comprising: code for performing coarse
detection and synchronization with respect to a received signal;
code for performing fine detection and synchronization for
acquisition of the received signal, wherein results of the coarse
detection and synchronization are used for the fine detection and
synchronization; and code for performing tracking mode processing
when the acquisition of the received signal has been achieved.
38. The computer-program product of claim 37, wherein the code for
performing the coarse detection and synchronization comprises: code
for performing coarse signal detection; code for performing coarse
preamble detection; code for performing coarse symbol boundary
detection; and code for performing fractional carrier frequency
offset estimation.
39. The computer-program product of claim 37, wherein the code for
performing the fine detection and synchronization comprises: code
for performing fine signal detection; code for performing fine
preamble detection; and code for performing fine symbol boundary
detection.
40. The computer-program product of claim 37, wherein the code for
performing the tracking mode processing comprises: code for
performing preamble sequence identification; code for performing
integer carrier frequency offset estimation; code for performing
segment estimation; code for performing sampling frequency offset
estimation; and code for performing physical layer
synchronization.
41. The computer-program product of claim 37, wherein the code for
performing the coarse detection and synchronization comprises code
for determining auto-correlation of the received signal using a
cyclic prefix property of a preamble.
42. The computer-program product of claim 37, wherein the code for
performing the fine detection and synchronization comprises code
for determining auto-correlation of at least one candidate preamble
signal using a conjugate symmetric property of a preamble.
43. The computer-program product of claim 37, wherein the code for
performing the fine detection and synchronization comprises code
for determining cross-correlation of a preamble with respect to a
reference preamble.
44. The computer-program product of claim 37, wherein the code for
performing the tracking mode processing comprises code for
determining cross-correlation between the received signal and
possible preamble sequences.
45. The computer-program product of claim 37, wherein the coarse
detection and synchronization and the fine detection and
synchronization are performed serially.
46. The computer-program product of claim 37, wherein the coarse
detection and synchronization and the fine detection and
synchronization are performed concurrently.
47. The computer-program product of claim 37, wherein the
computer-program product is configured for use within a wireless
device that is part of a wireless communication system that
utilizes orthogonal frequency division multiplexing.
48. The computer-program product of claim 37, wherein the
computer-program product is configured for use within a user
terminal.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to wireless
communication systems. More specifically, the present disclosure
relates to methods and apparatus for synchronization and detection
in wireless communication systems.
BACKGROUND
[0002] Wireless communication devices have become smaller and more
powerful in order to meet consumer needs and to improve portability
and convenience. Consumers have become dependent upon wireless
communication devices such as cellular telephones, personal digital
assistants (PDAs), laptop computers, and the like. Consumers have
come to expect reliable service, expanded areas of coverage, and
increased functionality. Wireless communication devices may be
referred to as mobile stations, stations, access terminals, user
terminals, terminals, subscriber units, user equipment, etc.
[0003] A wireless communication system may simultaneously support
communication for multiple wireless communication devices. A
wireless communication device may communicate with one or more base
stations (which may alternatively be referred to as access points,
Node Bs, etc.) via transmissions on the uplink and the downlink.
The uplink (or reverse link) refers to the communication link from
the wireless communication devices to the base stations, and the
downlink (or forward link) refers to the communication link from
the base stations to the wireless communication devices.
[0004] Wireless communication systems may be multiple-access
systems capable of supporting communication with multiple users by
sharing the available system resources (e.g., bandwidth and
transmit power). Examples of such multiple-access systems include
code division multiple access (CDMA) systems, time division
multiple access (TDMA) systems, frequency division multiple access
(FDMA) systems, and orthogonal frequency division multiple access
(OFDMA) systems.
[0005] As indicated above, the present disclosure relates generally
to wireless communication systems. More specifically, the present
disclosure relates to methods and apparatus for synchronization and
detection in wireless communication systems.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates an example of a wireless communication
system;
[0007] FIG. 2 illustrates an example of a transmitter and an
example of a receiver that may be used within a wireless
communication system that utilizes orthogonal frequency division
multiplexing (OFDM) and orthogonal frequency divisional multiple
access (OFDMA);
[0008] FIGS. 3A through 3D illustrate an example of a frame
structure for a wireless communication system that utilizes
OFDM/OFDMA;
[0009] FIG. 4 illustrates an example of an OFDMA frame in time
division duplex mode;
[0010] FIGS. 5A and 5B illustrate examples of preamble sequences
that may be defined for a wireless communication system that
utilizes OFDM/OFDMA;
[0011] FIG. 6 shows an example of a frequency domain downlink
preamble structure for a wireless communication system that
utilizes OFDM/OFDMA;
[0012] FIG. 7 illustrates an example of a downlink frame
prefix;
[0013] FIG. 8 illustrates an example of a synchronization and
detection method that may be performed by a wireless device in a
wireless communication system that utilizes OFDM/OFDMA;
[0014] FIG. 8A illustrates means-plus-function blocks corresponding
to the method shown in FIG. 8;
[0015] FIGS. 9 and 9A illustrate another example of a
synchronization and detection method that may be performed by a
wireless device in a wireless communication system that utilizes
OFDM/OFDMA;
[0016] FIGS. 10 and 10A illustrate means-plus-function blocks
corresponding to the method shown in FIGS. 9 and 9A;
[0017] FIG. 11 illustrates an example of a synchronization and
detection architecture for a wireless device in a wireless
communication system that utilizes OFDM/OFDMA; and
[0018] FIG. 12 illustrates various components that may be utilized
in a wireless device.
SUMMARY
[0019] A synchronization and detection method in a wireless device
is disclosed. The method may include performing coarse detection
and synchronization with respect to a received signal. The method
may also include performing fine detection and synchronization for
acquisition of the received signal. Results of the coarse detection
and synchronization may be used for the fine detection and
synchronization. The method may also include performing tracking
mode processing when the acquisition of the received signal has
been achieved.
[0020] A wireless device that performs synchronization and
detection with respect to a received signal is also disclosed. The
wireless device may include a coarse detection and synchronization
component that performs coarse detection and synchronization with
respect to a received signal. The wireless device may also include
a fine detection and synchronization component that performs fine
detection and synchronization for acquisition of the received
signal. Results of the coarse detection and synchronization may be
used for the fine detection and synchronization. The wireless
device may also include a tracking mode processing component that
performs tracking mode processing when the acquisition of the
received signal has been achieved.
[0021] An apparatus that performs synchronization and detection
with respect to a received signal is also disclosed. The apparatus
may include means for performing coarse detection and
synchronization with respect to a received signal. The apparatus
may also include means for performing fine detection and
synchronization for acquisition of the received signal. Results of
the coarse detection and synchronization may be used for the fine
detection and synchronization. The apparatus may also include means
for performing tracking mode processing when the acquisition of the
received signal has been achieved.
[0022] A computer-program product for performing synchronization
and detection with respect to a received signal is also disclosed.
The computer-program product may include a computer readable medium
having instructions thereon. The instructions may include code for
performing coarse detection and synchronization with respect to a
received signal. The instructions may also include code for
performing fine detection and synchronization for acquisition of
the received signal. Results of the coarse detection and
synchronization may be used for the fine detection and
synchronization. The instructions may also include code for
performing tracking mode processing when the acquisition of the
received signal has been achieved.
DETAILED DESCRIPTION
[0023] The methods and apparatus of the present disclosure may be
utilized in a broadband wireless communication system. The term
"broadband wireless" refers to technology that provides wireless,
voice, Internet, and/or data network access over a given area.
[0024] WiMAX, which stands for the Worldwide Interoperability for
Microwave Access, is a standards-based broadband wireless
technology that provides high-throughput broadband connections over
long distances. There are two main applications of WiMAX today:
fixed WiMAX and mobile WiMAX. Fixed WiMAX applications are
point-to-multipoint, enabling broadband access to homes and
businesses. Mobile WiMAX offers the full mobility of cellular
networks at broadband speeds.
[0025] Mobile WiMAX is based on OFDM (orthogonal frequency division
multiplexing) and OFDMA (orthogonal frequency division multiple
access) technology. OFDM is a digital multi-carrier modulation
technique that has recently found wide adoption in a variety of
high-data-rate communication systems. With OFDM, a transmit bit
stream is divided into multiple lower-rate sub-streams. Each
sub-stream is modulated with one of multiple orthogonal
sub-carriers and sent over one of a plurality of parallel
sub-channels. OFDMA is a multiple access technique in which users
are assigned sub-carriers in different time slots. OFDMA is a
flexible multiple-access technique that can accommodate many users
with widely varying applications, data rates, and quality of
service requirements.
[0026] The rapid growth in wireless internets and communications
has led to an increasing demand for high data rate in the field of
wireless communications services. OFDM/OFDMA systems are today
regarded as one of the most promising research areas and as a key
technology for the next generation of wireless communications. This
is due to the fact that OFDM/OFDMA modulation schemes can provide
many advantages like modulation efficiency, spectrum efficiency,
flexibility, and strong multipath immunity over conventional single
carrier modulation schemes.
[0027] IEEE 802.16x is an emerging standard organization to define
an air interface for fixed and mobile broadband wireless access
(BWA) systems. IEEE 802.16x approved "IEEE P802.16-REVd/D5-2004" in
May 2004 for fixed BWA systems and published "IEEE P802.16e/D12
Oct. 2005" in October 2005 for mobile BWA systems. Those two
standards defined four different physical layers (PHYs) and one
medium access control (MAC) layer. The OFDM and OFDMA physical
layer of the four physical layers are the most popular in the fixed
and mobile BWA areas respectively.
[0028] FIG. 1 illustrates an example of a wireless communication
system 100. The wireless communication system 100 may be a
broadband wireless communication system 100. The wireless
communication system 100 provides communication for a number of
cells 102, each of which is serviced by a base station 104. A base
station 104 may be a fixed station that communicates with user
terminals 106. The base station 104 may alternatively be referred
to as an access point, a Node B, or some other terminology.
[0029] FIG. 1 shows various user terminals 106 dispersed throughout
the system 100. The user terminals 106 may be fixed (i.e.,
stationary) or mobile. The user terminals 106 may alternatively be
referred to as remote stations, access terminals, terminals,
subscriber units, mobile stations, stations, user equipment, etc.
The user terminals 106 may be wireless devices, such as cellular
phones, personal digital assistants (PDAs), handheld devices,
wireless modems, laptop computers, personal computers, etc.
[0030] A variety of algorithms and methods may be used for
transmissions in the wireless communication system 100 between the
base stations 104 and the user terminals 106. For example, signals
may be sent and received between the base stations 104 and the user
terminals 106 in accordance with OFDM/OFDMA techniques. If this is
the case, the wireless communication system 100 may be referred to
as an OFDM/OFDMA system 100.
[0031] A communication link that facilitates transmission from a
base station 104 to a user terminal 106 may be referred to as a
downlink 108, and a communication link that facilitates
transmission from a user terminal 106 to a base station 104 may be
referred to as an uplink 110. Alternatively, a downlink 108 may be
referred to as a forward link or a forward channel, and an uplink
110 may be referred to as a reverse link or a reverse channel.
[0032] A cell 102 may be divided into multiple sectors 112. A
sector 112 is a physical coverage area within a cell 102. Base
stations 104 within an OFDM/OFDMA system 100 may utilize antennas
that concentrate the flow of power within a particular sector 112
of the cell 102. Such antennas may be referred to as directional
antennas.
[0033] FIG. 2 illustrates an example of a transmitter 202 that may
be used within a wireless communication system 100 that utilizes
OFDM/OFDMA. The transmitter 202 may be implemented in a base
station 104 for transmitting data 206 to a user terminal 106 on a
downlink 108. The transmitter 202 may also be implemented in a user
terminal 106 for transmitting data 206 to a base station 104 on an
uplink 110.
[0034] Data 206 to be transmitted is shown being provided as input
to a serial-to-parallel (S/P) converter 208. The S/P converter 208
splits the transmission data into N parallel data streams 210.
[0035] The N parallel data streams 210 may then be provided as
input to a mapper 212. The mapper 212 maps the N parallel data
streams 210 onto N constellation points. The mapping may be done
using some modulation constellation, such as binary phase-shift
keying (BPSK), quadrature phase-shift keying (QPSK), 8 phase-shift
keying (8PSK), quadrature amplitude modulation (QAM), etc. Thus,
the mapper 212 outputs N parallel symbol streams 216, each symbol
stream 216 corresponding to one of the N orthogonal sub-carriers of
the inverse fast Fourier transform (IFFT) 220. These N parallel
symbol streams 216 are represented in the frequency domain, and may
be converted into N parallel time domain sample streams 218 by an
IFFT component 220.
[0036] A brief note about terminology will now be provided. N
parallel modulations in the frequency domain are equal to N
modulation symbols in the frequency domain, which are equal to N
mapping plus N-point IFFT in the frequency domain, which is equal
to one (useful) OFDM symbol in the time domain, which is equal to N
samples in the time domain. One OFDM symbol in the time domain, Ns,
is equal to N.sub.cp (the number of guard samples per OFDM
symbol)+N (the number of useful samples per OFDM symbol).
[0037] The N parallel time domain sample streams 218 may be
converted into an OFDM/OFDMA symbol stream 222 by a
parallel-to-serial (P/S) converter 224. A guard insertion component
226 may insert a guard interval between successive OFDM/OFDMA
symbols in the OFDM/OFDMA symbol stream 222. The output of the
guard insertion component 226 may then be upconverted to a desired
transmit frequency band by a radio frequency (RF) front end 228. An
antenna 230 may then transmit the resulting signal 232.
[0038] FIG. 2 also illustrates an example of a receiver 204 that
may be used within a wireless communication system 100 that
utilizes OFDM/OFDMA. The receiver 204 may be implemented in a user
terminal 106 for receiving data 232' from a base station 104 on a
downlink 108. The receiver 204 may also be implemented in a base
station 104 for receiving data 232' from a user terminal 106 on an
uplink 110.
[0039] The transmitted signal 232 is shown traveling over a
wireless channel 234. When a signal 232' is received by an antenna
230', the received signal 232' may be downconverted to a baseband
signal by an RF front end 228'. A guard removal component 226' may
then remove the guard interval that was inserted between OFDM/OFDMA
symbols by the guard insertion component 226.
[0040] The output of the guard removal component 226' may be
provided to an S/P converter 224'. The S/P converter 224' may
divide the OFDM/OFDMA symbol stream 222' into the N parallel
time-domain symbol streams 218', each of which corresponds to one
of the N orthogonal sub-carriers. A fast Fourier transform (FFT)
component 220' converts the N parallel time-domain symbol streams
218' into the frequency domain, and outputs N parallel
frequency-domain symbol streams 216'.
[0041] A demapper 212' performs the inverse of the symbol mapping
operation that was performed by the mapper 212, thereby outputting
N parallel data streams 210'. A P/S converter 208' combines the N
parallel data streams 210' into a single data stream 206'. Ideally,
this data stream 206' corresponds to the data 206 that was provided
as input to the transmitter 202.
[0042] FIG. 3A illustrates an example of a frame 306 that may be
transmitted from a base station 104 to a user terminal 106 on a
downlink 108 within a wireless communication system 100 that
utilizes OFDM/OFDMA. The OFDM/OFDMA frame 306 is shown with respect
to a time axis 308. The OFDM/OFDMA frame 306 is shown with one
preamble symbol 310 and multiple data symbols 312. Although just
one preamble symbol 310 is shown in FIG. 3A, an OFDM/OFDMA frame
306 may include multiple preamble symbols 310.
[0043] FIGS. 3B and 3C illustrate examples of frequency domain
representations of a preamble symbol 310. These frequency domain
representations are shown with respect to a sub-carrier axis 316. A
used sub-carrier region 318 is shown. Two guard regions 320 are
also shown.
[0044] In FIG. 3B, the used sub-carrier region 318 includes pilot
sub-carriers 314a alternated with unmodulated sub-carriers 314b. In
FIG. 3C, each sub-carrier 314 in the used sub-carrier region 318 is
a pilot sub-carrier 314a.
[0045] FIG. 3D illustrates an example of a frequency domain
representation of a data symbol 312. The data symbol 312 includes
both data sub-carriers 314c and pilot sub-carriers 314a. A receiver
204 may perform channel estimation using pilot sub-carriers 314a of
a preamble symbol 310 and/or pilot sub-carriers 314a of a data
symbol 312.
[0046] The number of sub-carriers 314 within an OFDM/OFDMA system
100 may be equal to the number of FFT points. Within a wireless
communication system 100 that utilizes OFDM/OFDMA, all available
sub-carriers 314 may not be used. In particular, guard sub-carriers
314d in guard regions 320 may be excluded. In FIGS. 3B through 3D,
guard sub-carriers 314d are shown around the lower and higher
frequency bands. These guard sub-carriers 314d may not be allocated
for data sub-carriers 314c or pilot sub-carriers 314a.
[0047] FIG. 4 illustrates an example of an OFDMA frame 402 (with
only the mandatory zone) in time division duplex (TDD) mode. The
x-axis 404 denotes the time axis or the OFDMA symbol axis, and the
y-axis 406 denotes the frequency axis or the sub-channel axis. The
first symbol of the frame 402 is the downlink preamble 408, and
most of the timing reference is based on this preamble 408. The
first channel of the downlink sub-frame is called the frame control
header (FCH) 410, and the contents of the FCH 410 are called the
downlink frame prefix (DLFP). The following bursts 412 of the FCH
410 may include mobile application part (MAP) messages, control
messages, user bursts, etc.
[0048] The downlink radio signals from base stations 104 to user
terminals 106 may include voice or data traffic signals or both. In
addition, the base stations 104 generally transmit preambles 408 in
their downlink radio signals to identify to the user terminals 106
the corresponding cells 102 and corresponding segments in the cells
102 to which the downlink radio signals are directed. Such a
preamble 408 from a base station 104 allows a user terminal 106 to
synchronize its receiver 204 in both time and frequency with the
observed downlink signal and to acquire the identity of the base
station 104 that transmits the downlink signal.
[0049] In a wireless communication system 100 that is configured in
accordance with IEEE802.16e, there are three types of preamble
carrier sets that may be defined. The preamble carrier sets may be
defined by allocation of different sub-carriers 314, which may be
modulated using a boosted BPSK modulation with a specific
pseudo-noise (PN) code. The preamble carrier sets may be defined
using the following formula:
PA.sub.cset=s+3z (1)
[0050] In equation (1), the term PA.sub.cset represents all
sub-carriers 314 allocated to the specific preamble 408 based on
the useful sub-carrier index (i.e., an index that is assigned to
the sub-carriers 314 in the used sub-carrier region 318). The term
s represents the number of the preamble carrier set indexed 0 . . .
2 which corresponds to the segment of the sector 112. The term z
represents a running index starting from 0 to M-1, where M is the
length of the PN code. For example, M=284 at N=1024 FFT mode.
[0051] Each segment uses a preamble 408 corresponding to a carrier
set out of the three available carrier sets in the following
manner: segment 0 uses preamble carrier set 0, segment 1 uses
preamble carrier set 1, and segment 2 uses preamble carrier set 2.
(In the case of segment 0, the DC carrier is not modulated at all
and the appropriate PN is discarded. Therefore, the DC carrier is
zeroed. For the preamble symbol 408 there are 86 sub-carriers 314
in the guard regions 320 on the left side and the right side of the
spectrum.) For a 1024 FFT size the PN series modulating the
preamble carrier set is defined in the standard specification for
an IEEE802.16e OFDM/OFDMA system.
[0052] FIGS. 5A and 5B illustrate examples of preamble sequences
506a, 506b that may be defined for a wireless communication system
100 that is configured in accordance with IEEE 802.16e. These
preamble sequences 506a, 506b are defined in the standard
specification for an IEEE 802.16e OFDM/OFDMA system.
[0053] The preamble sequences 506a shown in FIG. 5A correspond to
an IEEE 802.16e OFDM/OFDMA system that uses 1024 sub-carriers. In
the case of segment 0, the DC carrier may not be modulated at all
and the appropriate PN may be discarded; therefore, the DC carrier
may always be zeroed. For the preamble symbol 408 there may be 86
sub-carriers 314 in the guard regions 320 on the left side and the
right side of the spectrum.
[0054] The preamble sequences 506b shown in FIG. 5B correspond to
an IEEE 802.16e OFDM/OFDMA system that uses 512 sub-carriers. In
the case of segment 1, the DC carrier may not be modulated at all
and the appropriate PN may be discarded; therefore, the DC carrier
may always be zeroed. For the preamble symbol 408 there may be 42
sub-carriers 314 in the guard regions 320 on the left side and the
right side of the spectrum.
[0055] Each preamble sequence 506a, 506b is associated with a
segment 510a, 510b. Each preamble sequence 506a, 506b is also
associated with a cell 102, which is identified by a cell
identifier (IDcell) 512a, 512b. Each preamble sequence 506a, 506b
is also associated with an index 516a, 516b, which may be referred
to as a preamble index 516a, 516b.
[0056] The preamble sequence (PN series) 506 modulating the
preamble carrier sets are defined in the standard specification for
an IEEE 802.16e OFDM/OFDMA system. The preamble sequence 506 that
is modulated depends on the segment 510 that is used and the IDcell
parameter 512. The defined preamble sequence 506 may be mapped onto
the preamble sub-carriers 314 in ascending order. The tables shown
in FIGS. 5A and 5B include the preamble sequences 506 in a
hexadecimal format. The value of the PN may be obtained by
converting the series to a binary series (Wk) and mapping the PN
from the most significant bit (MSB) of each symbol to the least
significant bit (LSB). A "0" may be mapped to "+1," and a "1" may
be mapped to "-1." For example, for index=0, segment=0,
Wk=110000010010 . . . , and the mapping maybe: -1 -1 +1 +1 +1 +1 +1
-1 +1 +1 -1 +1 . . . A total of 114 PN series (N.sub.pn=114) are
defined in the standard specification, or 38 PN series for each
segment (N.sub.pnseg=38, N.sub.seg=3).
[0057] FIG. 6 shows a frequency domain representation of a downlink
preamble 608 for an IEEE802.16e OFDM/OFDMA system with an FFT size
of 1024. In FIG. 6, N stands for a null sub-carrier 314, S0 stands
for a sub-carrier 314 which belongs to segment 0, S1 stands for a
sub-carrier 314 which belongs to segment 1, S2 stands for a
sub-carrier 314 which belongs to segment 2, and dc stands for a DC
sub-carrier 314. Because the FFT size is 1024, there are 1024
sub-carriers 314, and these sub-carriers 314 are numbered from SC1
to SC1024.
[0058] FIG. 7 illustrates a 24-bit downlink frame prefix (DLFP)
702. The frame control header (FCH) 410, which was discussed above,
is an important channel (or burst) of an IEEE802.16d/e system. The
contents of the FCH 410 are called the downlink frame prefix (DLFP)
702. The DLFP 702 is a data structure that is transmitted at the
beginning of each frame 402. The DLFP 702 contains information
regarding the current frame 402 and is mapped to the FCH 410.
Successful decoding of the FCH/DLFP 410, 702 may be important to
process the entire frame 402.
[0059] To decode downlink messages or bursts 412 sent by the base
station 104, the user terminal 106 may perform the following
functions before FCH decoding: automatic gain control (AGC),
downlink signal detection, downlink preamble detection, frequency
synchronization (fractional and integer), OFDM symbol timing
detection, segment detection, and preamble sequence detection.
[0060] The present disclosure relates generally to a
synchronization and detection architecture for a wireless
communication system 100 that utilizes OFDM/OFDMA. The proposed
scheme may include three major steps. The first step may include
coarse detection and synchronization processes, which may include
coarse signal detection, coarse preamble detection, coarse symbol
timing detection, and fractional frequency offset estimation. The
second step may include fine detection and synchronization
processes, which may include verification of signal detection,
verification of preamble detection, and fine symbol timing
detection. The third step may include preamble sequence
identification and integer frequency offset estimation processes,
which may include preamble sequence identification, integer
frequency offset estimation, segment extraction, and sampling
frequency offset estimation. An automatic gain control (AGC)
process may also be included as one of the synchronization
processes, and a physical layer (PHY) synchronization process may
also be included for acquiring the downlink PHY synchronization
that is the final stage of PHY level synchronization. In addition,
the present disclosure also includes a scheme for searching
neighbor cells for purposes of handover.
[0061] FIG. 8 illustrates an example of a synchronization and
detection method 800 that may be performed by a wireless device
(e.g., a user terminal 106) in a wireless communication system 100
that utilizes OFDM/OFDMA.
[0062] The method 800 may include performing 802 coarse signal
detection with respect to a received signal, performing 804 coarse
preamble detection with respect to the received signal, performing
806 coarse symbol boundary detection with respect to the received
signal, and performing 808 fractional carrier frequency offset
(CFO) estimation with respect to the received signal. Collectively,
these steps 802, 804, 806, 808 may be referred to as performing 810
coarse detection and synchronization with respect to a received
signal.
[0063] The method 800 may also include performing 812 fine signal
detection with respect to the received signal, performing 814 fine
preamble detection with respect to the received signal, and
performing 816 fine symbol boundary detection with respect to the
received signal. Collectively, these steps 812, 814, 816 may be
referred to as performing 818 fine detection and synchronization
for acquisition of the received signal.
[0064] The results that are determined from performing 810 the
coarse detection and synchronization may be used for performing 818
the fine detection and synchronization. For example, performing 812
fine signal detection may include verifying the result that was
obtained by performing 802 coarse signal detection. Similarly,
performing 814 fine preamble detection may include verifying the
result that was obtained by performing 804 coarse preamble
detection.
[0065] When the acquisition of the received signal has been
completed, tracking mode may be entered. In particular, the method
800 may then include performing 820 preamble sequence
identification, performing 822 integer carrier frequency offset
(CFO) estimation, performing 824 segment estimation, performing 826
sampling frequency offset (SFO) estimation, and performing 828
physical layer synchronization. Collectively, these steps 820, 822,
824, 826, 828 may be referred to as performing 830 tracking mode
processing.
[0066] The method 800 of FIG. 8 described above may be performed by
various hardware and/or software component(s) and/or module(s)
corresponding to the means-plus-function blocks 800A illustrated in
FIG. 8A. In other words, blocks 802 through 828 illustrated in FIG.
8 correspond to means-plus-function blocks 802A through 828A
illustrated in FIG. 8A.
[0067] FIGS. 9 and 9A illustrate an example of a synchronization
and detection method 900 that may be performed by a wireless device
(e.g., a user terminal 106) in a wireless communication system 100
that utilizes OFDM/OFDMA. This method 900 is an example of a
possible implementation of the synchronization and detection method
800 that is shown in FIG. 8.
[0068] The method 900 includes performing 902 parameter setting and
adjustment. This may include setting bandwidth, setting frame
duration, setting fast Fourier transform (FFT) size, setting Gr,
setting automatic gain control (AGC), setting and starting timers,
setting acquisition mode parameters, setting tracking mode
parameters, setting physical layer synchronized mode parameters,
etc. The term Gr refers to guard ratio, which is one of 1/32, 1/16,
1/8, and 1/4 of a useful OFDMA symbol.
[0069] The method 900 also includes entering 904 acquisition mode
906 or tracking mode 908. In acquisition mode 906, timing
information and base station information may not be available. Some
parameters like threshold(s), timing, preamble sequence 506, and
frequency offset may be set based on acquisition mode parameter
control. In acquisition mode 906, detectors and synchronizers may
continue the same processes as previous operations for all possible
timing hypotheses until acquisition is verified.
[0070] In tracking mode 908, some timing and frequency information
may be available, so that information may be used in subsequent
processes. Some parameters like threshold(s), timing, preamble
sequence 506, and frequency offset may be set based on tracking
mode parameter control. Those parameters may be fine tuned over
time. In tracking mode 908, detectors and synchronizers may
continue the same processes by updating synchronization and
detection parameters to the values obtained during fine
synchronization and detection. The timing hypotheses may be
narrowed more and more to a given range over time.
[0071] The method 900 also includes performing 910 coarse detection
and synchronization. As indicated above, coarse detection and
synchronization may include coarse signal detection, coarse
preamble detection, coarse symbol boundary detection, and
fractional CFO estimation.
[0072] Once an incoming signal is recognized 912 as a candidate,
then the candidate may be delivered 914 to the appropriate
component(s) for fine detection and synchronization with related
information like timing and frequency offset. For purposes of
performing 910 coarse detection and synchronization, the incoming
signal may be processed on a symbol-by-symbol basis, thereby
providing real-time processing capability. In one implementation,
every incoming OFDMA symbol may be considered 912 to be a
candidate, and all the candidates may be delivered 914 to the
appropriate component(s) for fine detection and
synchronization.
[0073] Certain information may be determined as part of performing
910 coarse detection and synchronization. For example, the average
power of the received signal may be determined. This may be
referred to herein as AP. As another example, the auto-correlation
of the received signal using the cyclic prefix (CP) property of the
preamble may be determined. This may be referred to herein as
CORRcp. Both AP and CORRcp may be determined on a continuous basis.
CORRcp may be determined in the time domain.
[0074] As indicated above, performing 910 coarse detection and
synchronization may include performing coarse signal detection.
Both AP and CORRcp may be used as part of a threshold detection
scheme for purposes of coarse signal detection. For example, the
measured AP and CORRcp values may be compared to predetermined
thresholds for purposes of coarse signal detection.
[0075] As indicated above, performing 910 coarse detection and
synchronization may include performing coarse preamble detection.
Both AP and CORRcp may be used as part of a threshold detection
scheme for purposes of coarse preamble detection. For example, the
measured AP and CORRcp values may be compared to predetermined
thresholds for purposes of coarse preamble detection. Also, because
the power may be increased (e.g., by about 4.26 dB) for
transmission of the preamble 408, this may also be taken into
consideration for purposes of coarse preamble detection.
[0076] All possible preamble candidates may be delivered 914 to the
appropriate component(s) for purposes of fine detection and
synchronization. This may be done on a continuous basis.
[0077] As indicated above, performing 910 coarse detection and
synchronization may include performing coarse symbol boundary
detection. Both AP and CORRcp may be used as part of a threshold
detection scheme for purposes of coarse symbol boundary detection.
For example, the measured AP and CORRcp values may be compared to
predetermined thresholds for purposes of coarse symbol boundary
detection. Coarse symbol boundary detection may include determining
a possible range for an initial timing hypothesis. This initial
timing hypothesis may be referred to herein as n.sub.0. This range
may be delivered 914 to the appropriate component(s) for purposes
of fine detection and synchronization.
[0078] A brief explanation will now be provided about how the
thresholds for coarse signal detection, coarse preamble detection,
and coarse symbol boundary detection are determined. The cyclic
prefix correlation metric may be expressed as:
CORR cp ( m ) = k = m m + N g - 1 r ( k ) r * ( k + N ) ( 2 )
##EQU00001##
[0079] The average power metric may be expressed as:
AP ( m ) = k = m m + N g - 1 r ( k + N ) 2 ( 3 ) ##EQU00002##
[0080] For coarse signal detection, the following tests may be used
with some state machine:
{ Hit = 1 if CORR cp ( m ) >= F sig det .times. AP ( m ) Hit = 0
otherwise and / or ( 4 ) { Hit = 1 if AP ( m ) >= F sig det bgn
.times. AP bgn Hit = 0 otherwise ( 5 ) ##EQU00003##
[0081] For coarse preamble detection, the following tests may be
used with some stat machine:
{ Hit = 1 if CORR cp ( m ) >= F pa det .times. AP ( m ) Hit = 0
otherwise ( 6 ) ##EQU00004##
[0082] For coarse symbol boundary detection, the following maximum
likelihood test may be used:
n 0 = arg max m ( CORR cp ( m ) ) ( 7 ) ##EQU00005##
[0083] F.sub.sigdet and F.sub.padet are factors for signal
detection, preamble detection and coarse symbol boundary detection,
respectively. F.sub.sigdetbgn and AP.sub.bgn are factors for signal
detection and average background noise level, respectively.
[0084] As indicated above, performing 910 coarse detection and
synchronization may include performing fractional carrier frequency
offset (CFO) estimation. CORRcp may be used for purposes of
fractional CFO estimation. An example of an estimation range that
may be used is -0.5 to +0.5. The fractional CFO estimate that is
determined may be delivered 914 to the appropriate component(s) for
purposes of fractional CFO compensation if tracking mode 908 is
activated.
[0085] The method 900 also includes performing 916 fine detection
and synchronization. In general terms, fine detection and
synchronization may be thought of as verifying some or all of the
results of coarse detection and synchronization. As indicated
above, fine detection and synchronization may include fine signal
detection, fine preamble detection, and fine symbol boundary
detection.
[0086] One goal of fine detection and synchronization may be to
recognize 918 an incoming candidate desired signal. Once this
occurs, then it may be determined that acquisition is complete, and
tracking mode 908 may be entered 920.
[0087] When fine synchronization is performed 916, all candidates
that are determined as a result of performing 910 coarse
synchronization may be processed. Incoming candidates may be
processed on a symbol-by-symbol basis. All fine detection and
synchronization may be done within one symbol to provide a
real-time processing capability.
[0088] Fine detection and synchronization may be performed
regardless of whether the preamble 408 is known or unknown. The
following discussion of fine detection and synchronization may be
applicable during acquisition mode 906, during tracking mode 908,
or during normal operation.
[0089] Certain information may be determined as part of performing
916 fine detection and synchronization. For example, the average
power of the received signal may be determined. As indicated above,
the average power may be referred to herein as AP. As another
example, the auto-correlation of delivered candidate preamble
signal(s) using the conjugate symmetric (CS) property of the
preamble 408 may be determined. This may be referred to herein as
CORRcs. AP and CORRcs may be determined continuously for all
delivered candidates.
[0090] A brief description will now be provided regarding how the
CORRcs may be determined. A candidate preamble signal and the
timing hypothesis n.sub.0 may be received. The FFT may be applied
for each half of the preamble 408. The symbol boundary may be
referenced by the timing hypothesis n.sub.0. The convolution
function may be provided by dot-multiplying each corresponding
sub-carrier 314 in the frequency domain. The IFFT may then be
applied to the result. CORRcs may be determined in the time domain
or in the frequency domain.
[0091] As indicated above, performing 916 fine detection and
synchronization may include performing fine signal detection. Both
AP and CORRcs may be used as part of a threshold detection scheme
for purposes of fine signal detection. For example, the measured AP
and CORRcp values may be compared to predetermined thresholds for
purposes of fine signal detection.
[0092] As indicated above, performing 916 fine detection and
synchronization may include performing fine preamble detection.
Both AP and CORRcs may be used as part of a peak detection and/or a
threshold detection scheme for purposes of fine preamble detection.
For example, the measured AP and CORRcs values may be compared to
predetermined thresholds for purposes of fine preamble
detection.
[0093] The result of the fine preamble detection may be used for
purposes of performing fine signal detection. For fine symbol
boundary detection, peak detection may be used. This may be
expressed as:
FineSymBoundry z fsb = arg max n ( CORR cs ( n ) ) ( 8 )
##EQU00006##
[0094] The term z.sub.fsigdet is the position of the fine symbol
boundary. For fine signal detection, threshold detection may be
used. In particular, CORR.sub.cs (z.sub.fsb) and AP may be
compared. This may be expressed as:
FineSigDet = { 1 if CORR cs ( z fsb ) .gtoreq. F fsig det .times.
AP 0 otherwise ( 9 ) ##EQU00007##
[0095] The term F.sub.fsigdet is a factor for fine signal
detection. If the fine signal detection passes the criteria, it may
be determined that the coarse signal detection has been verified,
the signal has been detected, and that the fine symbol boundary
z.sub.fsb is valid and final. The method 900 may then proceed to
the next stage (i.e., processing the preamble sequence
identification). If the fine signal detection fails the criteria,
it may be determined that the coarse signal detection was wrong and
that the signal has not been detected yet. Then, the coarse
synchronization processes may be redone.
[0096] As indicated above, performing 916 fine detection and
synchronization may include performing fine symbol boundary
detection. Both AP and CORRcs may be used as part of a peak
detection scheme for purposes of fine symbol boundary detection.
The fine symbol boundary (timing) may be determined using the
result of the peak detection and the initial timing hypothesis
n.sub.0 that was determined as part of coarse detection and
synchronization.
[0097] As discussed above, fractional CFO estimation may be
performed as part of coarse detection and synchronization.
Fractional CFO estimation may also be performed as part of fine
detection and synchronization. As discussed above, CORRcp may be
used for purposes of fractional CFO estimation, depending on and
based on the results of fine signal detection, fine preamble
detection, and fine symbol boundary detection. An example of an
estimation range that may be used is -0.5 to +0.5.
[0098] Next, fine detection and synchronization will be discussed
assuming that the preamble 408 is known. This may be the case after
acquisition has been completed (i.e., after tracking mode 908 has
been entered), or during normal operation. This case may be
applicable for searching neighbor cells.
[0099] If the preamble 408 is known, performing 916 fine detection
and synchronization may also include determining the
cross-correlation of the preamble 408 with respect to a reference
preamble. This may be referred to herein as CORRref. CORRref may be
determined only once per frame.
[0100] If the preamble 408 is known and CORRref is determined,
CORRref may be used for purposes of fine preamble detection and
fine symbol boundary detection. The results of the fine preamble
detection and the fine symbol boundary detection may be listed on
candidate neighbor lists.
[0101] The method 900 may also include performing 922 fractional
carrier frequency offset (CFO) compensation. This may be done after
entering tracking mode 908, i.e., fractional CFO compensation may
not be available in acquisition mode 906. Fractional CFO
compensation may be applied for all incoming signals. Fractional
CFO compensation may be realized only in the baseband signal, only
in the RF signal, or in both the baseband signal and the RF signal.
Fractional CFO compensation may be performed in the time
domain.
[0102] The method 900 may also include performing 924 a fast
Fourier transform (FFT) for all incoming signals that are processed
in the frequency domain. If the FFT is performed before acquiring
physical layer synchronization, it may be sufficient to apply the
FFT to only the candidate preamble signal. Different FFT modes may
be supported (e.g., 1024 mode, 512 mode). The resulting signal
(after the FFT is performed 924) may be saved in a signal
buffer.
[0103] Referring now to FIG. 9A, the method 900 may also include
performing 926 preamble sequence identification and integer carrier
frequency offset (CFO) estimation. A two-step approach may be used
to reduce the search time during preamble sequence identification
and integer CFO estimation. The first step may include reducing
possible integer CFO candidates. The second step may include
searching for all possible candidates of preamble sequences 506,
for the reduced set of integer CFO candidates. All searching
operations for preamble sequence identification and integer CFO
estimation may be done within one frame in order to provide
real-time processing.
[0104] As part of performing 926 preamble sequence identification
and integer CFO estimation, certain information may be determined.
For example, the power of each sub-carrier 314 may be determined.
In addition, the cross-correlation between the received signal and
possible preamble sequences 506 may also be determined. This may be
referred to herein as CORRps.
[0105] Performing 926 preamble sequence identification and integer
CFO estimation may also include making a decision about a virtual
segment. This decision may be made using the measured power of each
sub-carrier 314. The power sum of each virtual segment (Pv0, Pv1,
Pv2) may be computed. Peak detection may be used to decide on the
virtual segment. The candidates of the integer CFO may be reduced
based on the virtual segment. The candidates may be reduced by
one-third, for example.
[0106] As indicated above, CORRps may be determined as part of
performing 926 preamble sequence identification and integer CFO
estimation. This may be done before acquiring physical layer
synchronization. In this case, CORRps may be computed for all
possible preamble sequences (e.g., 114 sequences where the FFT mode
is 1024). Alternatively, CORRps may be determined after acquiring
physical layer synchronization or during a cell search process.
[0107] CORRps may be determined for all integer CFO candidates
within the reduced set of integer CFO candidates. This may be done
either before or after acquiring physical layer synchronization.
There may be Zi/3 integer CFO candidates per preamble sequence 506,
where Zi is the maximum allowable integer CFO value.
[0108] Performing 926 preamble sequence identification and integer
CFO estimation may be done using peak detection for all the results
of CORRps. The PAindex 516 and the cell ID 512 may be determined.
In addition, the segment 510 may be determined. In addition, the
integer CFO may be determined.
[0109] The method 900 may also include performing 928 overall CFO
estimation and compensation. The overall CFO estimate may include
both the fractional CFO estimate and the integer CFO estimate.
Overall CFO compensation may be performed based on the estimated
overall CFO. Overall CFO compensation may be realized only in the
baseband signal, only in the RF signal, or both in the baseband
signal and the RF signal. Overall CFO compensation may be performed
in the time domain.
[0110] The method 900 may also include performing 930 sampling
frequency offset (SFO) estimation and compensation. The SFO may be
extracted from the estimated CFO. As an example, in mobile WiMAX a
locked clock scheme may be used for SFO estimation. SFO
compensation may be performed using the estimated SFO. SFO
compensation may be realized only in the baseband signal, only in
the RF signal, or both in the baseband signal and the RF signal.
SFO compensation may be performed in the time domain.
[0111] The method 900 may also include acquiring 932 physical layer
synchronization. This may include determining whether all
hypotheses are correct or not. An attempt may be made to receive
downlink messages including FCH/DLFP, MAP messages, Device
Capability Discovery (DCD) messages, Uniform Call Distribution
(UCD) messages, and so forth. It may be determined 934 that
physical layer synchronization has been established if received
messages look like downlink messages by checking the cyclic
redundancy check (CRC) or the message rules of the downlink
108.
[0112] If after investigating downlink messages (which may be done
for several frames repeatedly) it is determined 934 that physical
layer synchronization is not established, then the method 900 may
include going back to acquisition mode 906 and retrying the entire
synchronization process again. In particular, the wireless device
may be set to acquisition mode 906, parameters may be set 902 for
acquisition mode 906, and the method 900 may continue in the manner
described above.
[0113] If after investigating downlink messages it is determined
934 that physical layer synchronization is established (e.g., if
downlink messages are received successfully), then the method 900
may include entering 936 normal operation. In particular, the
wireless device may be set to physical layer synchronization mode,
and parameters may be set for physical layer synchronization.
[0114] Normal operation 936 may include estimating and compensating
for CFO/SFO continuously. Normal operation 936 may also include
performing channel estimation and equalization from the preamble
408 to the end of the downlink sub-frame.
[0115] Normal operation 936 may also include FCH/DLFP processing.
This may include estimating the sub-channel bitmap before decoding
the FCH/DLFP. This may also include extracting the zone boosting
factor and available pilots from the estimated sub-channel bitmap.
The FCH/DLFP may be decoded, and the sub-channel bitmap may be
extracted from the decoded DLFP. The zone boosting factor and
available pilots may be extracted from the sub-channel bitmap.
Normal operation may also include downlink 108/uplink 110 map
processing, burst processing, acquiring all necessary downlink
parameters from the base station 104, entering a ranging process,
and so forth.
[0116] Coarse detection and synchronization and fine detection and
synchronization may be performed serially. In other words, the
coarse detection and synchronization may be performed first, and
then the fine detection and synchronization may be performed when
the results of the coarse detection and synchronization are
available.
[0117] Alternatively, coarse detection and synchronization and fine
detection and synchronization may be performed concurrently. In
other words, the coarse detection and synchronization and the fine
detection and synchronization may begin at about the same time.
Initially, the fine detection and synchronization may be performed
without any results from the coarse detection and synchronization.
When results from the coarse detection and synchronization are
available, these results may be used for purposes of the fine
detection and synchronization.
[0118] The method 900 of FIGS. 9 and 9A described above may be
performed by various hardware and/or software component(s) and/or
module(s) corresponding to the means-plus-function blocks 1000
illustrated in FIGS. 10 and 10A. In other words, blocks 902 through
936 illustrated in FIGS. 9 and 9A correspond to means-plus-function
blocks 1002 through 1036 illustrated in FIGS. 10 and 10A.
[0119] FIG. 11 illustrates an example of a synchronization and
detection architecture 1100 for a wireless device (e.g., a user
terminal 106), which may be part of a wireless communication system
100 that utilizes OFDM/OFDMA. The synchronization and detection
architecture 1100 may be used to implement the methods 800, 900
shown in FIGS. 8 and 9-9A.
[0120] The synchronization and detection architecture 1100 includes
a component 1106 that performs coarse signal detection. This
component 1106 may be referred to as a coarse signal detection
component 1106. Coarse signal detection may be performed in the
manner described above in relation to the methods 800, 900 shown in
FIGS. 8 and 9-9A.
[0121] The synchronization and detection architecture 1100 also
includes components 1108a, 1108b that perform coarse preamble
detection. These components 1108a, 1108b may be referred to
collectively as a coarse preamble detection component 1108. Coarse
preamble detection may be performed in the manner described above
in relation to the methods 800, 900 shown in FIGS. 8 and 9-9A.
[0122] The synchronization and detection architecture 1100 also
includes a component 1110 that performs coarse symbol boundary
detection. This component 1110 may be referred to as a coarse
symbol boundary detection component 1110. Coarse symbol boundary
detection may be performed in the manner described above in
relation to the methods 800, 900 shown in FIGS. 8 and 9-9A.
[0123] The synchronization and detection architecture 1100 also
includes a component 1112 that performs fractional CFO estimation.
This component 1112 may be referred to as a fractional CFO
estimation component 1112. Fractional CFO estimation may be
performed in the manner described above in relation to the methods
800, 900 shown in FIGS. 8 and 9-9A.
[0124] The coarse signal detection component 1106, coarse preamble
detection component 1108, coarse symbol boundary detection
component 1110, and fractional CFO estimation component 1112 may be
referred to collectively as a coarse detection and synchronization
component 1102. Coarse detection and synchronization may be
performed in the manner described above in relation to the methods
800, 900 shown in FIGS. 8 and 9-9A.
[0125] The synchronization and detection architecture 1100 also
includes a component 1128 that determines CORRcp (i.e., the
auto-correlation of the received signal 1104 using the cyclic
prefix (CP) property of the preamble 408, as described above). This
component 1128 may be referred to herein as a cyclic prefix-based
auto-correlation component 1128. CORRcp may be determined in the
manner described above in relation to the methods 800, 900 shown in
FIGS. 8 and 9-9A.
[0126] The synchronization and detection architecture 1100 also
includes a component 1144 that determines AP (i.e., the average
power of the received signal 1104, as described above). This
component 1144 may be referred to herein as an average power
determination component 1144. AP may be determined in the manner
described above in relation to the methods 800, 900 shown in FIGS.
8 and 9-9A.
[0127] The synchronization and detection architecture 1100 also
includes a component 1118 that performs fine signal detection. This
component 1118 may be referred to herein as a fine signal detection
component 1118. Fine signal detection may be performed in the
manner described above in relation to the methods 800, 900 shown in
FIGS. 8 and 9-9A.
[0128] The synchronization and detection architecture 1100 also
includes a component 1120 that performs fine preamble detection.
This component 1120 may be referred to herein as a fine preamble
detection component 1120. Fine preamble detection may be performed
in the manner described above in relation to the methods 800, 900
shown in FIGS. 8 and 9-9A.
[0129] The synchronization and detection architecture 1100 also
includes a component 1122 that performs fine symbol boundary
detection. This component 1122 may be referred to herein as a fine
symbol boundary detection component 1122. Fine symbol boundary
detection may be performed in the manner described above in
relation to the methods 800, 900 shown in FIGS. 8 and 9-9A.
[0130] The fine signal detection component 1118, fine preamble
detection component 1120, and fine symbol boundary detection
component 1122 may be referred to collectively as a fine detection
and synchronization component 1114. Fine detection and
synchronization may be performed in the manner described above in
relation to the methods 800, 900 shown in FIGS. 8 and 9-9A.
[0131] As indicated above, results 1116 of the coarse detection and
synchronization may be used for the fine detection and
synchronization. For example, once an incoming signal is recognized
as a candidate, then the candidate may be delivered to the fine
detection and synchronization component 1114 with related
information like timing and frequency offset. Thus, the results
1116 of the coarse detection and synchronization that are used for
the fine detection and synchronization may include one or more
candidate signals, and related information like timing information
and frequency offset information corresponding to the candidate
signal(s).
[0132] The synchronization and detection architecture 1100 also
includes a component 1124 that determines CORRcs (i.e., the
auto-correlation of delivered candidate preamble signal(s) using
the conjugate symmetric (CS) property of the preamble 408, as
described above). This component 1124 may be referred to herein as
a conjugate symmetric-based auto-correlation component 1124. CORRcs
may be determined in the manner described above in relation to the
methods 800, 900 shown in FIGS. 8 and 9-9A.
[0133] As indicated above, CORRcs may be determined in the time
domain or in the frequency domain. FIG. 11 shows CORRcs being
determined in the frequency domain.
[0134] The synchronization and detection architecture 1100 also
includes a component 1126 that determines CORRref (i.e., the
cross-correlation of the preamble 408 with respect to a reference
preamble, as described above). This component 1126 may be referred
to herein as a reference cross-correlation component 1126. CORRref
may be determined in the manner described above in relation to the
methods 800, 900 shown in FIGS. 8 and 9-9A.
[0135] The synchronization and detection architecture 1100 also
includes various components that may be utilized when the
acquisition of the received signal 1104 has been achieved (i.e.,
when tracking mode 908 has been entered). Collectively, these
components may be referred to as a tracking mode processing
component 1130.
[0136] The tracking mode processing component 1130 includes a
component 1146 that performs the fast Fourier transform (FFT). This
component 1146 may be referred to as an FFT component 1146.
[0137] The tracking mode processing component 1130 also includes a
signal buffer 1148. The signal buffer 1148 may be used to store the
output of the FFT component 1146.
[0138] The tracking mode processing component 1130 also includes a
component 1150 that determines the power of each sub-carrier 314.
This component 1150 may be referred to as a sub-carrier power
calculation component 1150.
[0139] The tracking mode processing component 1130 also includes a
component 1152 that determines a virtual segment for purposes of
identifying a reduced set of integer CFO candidates. This component
1152 may be referred to as a virtual segment decision component
1152. The virtual segment may be determined in the manner described
above in relation to the methods 800, 900 shown in FIGS. 8 and
9-9A.
[0140] The tracking mode processing component 1130 also includes a
component 1154 that identifies a reduced set of integer CFO
candidates based on the virtual segment that is identified. This
component 1154 may be referred to as a candidate reduction
component 1154. The reduced set of integer CFO candidates may be
determined in the manner described above in relation to the methods
800, 900 shown in FIGS. 8 and 9-9A.
[0141] The tracking mode processing component 1130 also includes a
component 1156 that determines CORRps (i.e., the cross-correlation
between the received signal 1104 and possible preamble sequences
506, as discussed above). This component 1156 may be referred to as
a preamble sequence cross-correlation component 1156. CORRps may be
determined in the manner described above in relation to the methods
800, 900 shown in FIGS. 8 and 9-9A.
[0142] The tracking mode processing component 1130 also includes a
component 1132 that performs preamble sequence identification,
i.e., that identifies the preamble sequence 506 within the signal
1104 that is received from the base station 104. This component
1132 may be referred to herein as a preamble sequence
identification component 1132. Preamble sequence identification may
be performed in the manner described above in relation to the
methods 800, 900 shown in FIGS. 8 and 9-9A.
[0143] The tracking mode processing component 1130 also includes a
component 1134 that performs segment estimation, i.e., that
determines the segment to which the transmitting base station 104
corresponds. This component 1134 may be referred to herein as a
segment estimation component 1134. Segment estimation may be
performed in the manner described above in relation to the methods
800, 900 shown in FIGS. 8 and 9-9A.
[0144] The tracking mode processing component 1130 also includes a
component 1136 that performs integer CFO estimation, i.e., that
determines the integer CFO of the received signal 1104. This
component 1136 may be referred to herein as an integer CFO
estimation component 1136. Integer CFO estimation may be performed
in the manner described above in relation to the methods 800, 900
shown in FIGS. 8 and 9-9A.
[0145] The tracking mode processing component 1130 also includes a
component 1138 that performs overall CFO estimation, i.e., that
determines the overall CFO (both integer CFO and fractional CFO) of
the received signal 1104. This component 1138 may be referred to
herein as an overall CFO estimation component 1138. Overall CFO
estimation may be performed in the manner described above in
relation to the methods 800, 900 shown in FIGS. 8 and 9-9A.
[0146] The tracking mode processing component 1130 also includes a
component 1140 that performs sampling frequency offset (SFO)
estimation. This component 1140 may be referred to as an SFO
estimation component 1140. SFO estimation may be performed in the
manner described above in relation to the methods 800, 900 shown in
FIGS. 8 and 9-9A.
[0147] The tracking mode processing component 1130 also includes a
component 1142 that performs physical layer (PHY) synchronization.
This component 1142 may be referred to as a physical layer
synchronization component 1142. Physical layer synchronization may
be performed in the manner described above in relation to the
methods 800, 900 shown in FIGS. 8 and 9-9A.
[0148] The synchronization and detection architecture 1100 also
includes a component 1178 that performs CFO/SFO compensation. This
component 1178 may be referred to as a CFO/SFO compensation
component 1178. CFO/SFO compensation may be performed in the manner
described above in relation to the methods 800, 900 shown in FIGS.
8 and 9-9A.
[0149] A neighbor cell search capability may be provided during
normal operation 936. The neighbor cell search capability will now
be described briefly.
[0150] During normal operation after acquiring all needed
synchronization for the serving cell, the neighbor cell's
information (especially focused on preamble sequences for
synchronization purposes or cell search purposes) may or may not be
known from the serving base station 104. One of two approaches may
be used for a neighbor cell search. One approach is to use CORRref
(cross-correlation using the reference preamble pattern) using time
domain processing, and the other is to use CORRcs (conjugate
symmetric based correlation) and preamble sequence identification
using frequency/time domain processing.
[0151] The first scheme (CORRref based) may be used when the user
terminal 106 knows the neighbor cell's information so the user
terminal 106 knows the neighbor cell's preamble sequences that are
used in the corresponding base stations 104. Based on the known
preamble sequences, the user terminal 106 may search the neighbor
cell's timing (symbol boundary) using a CORRref correlator.
[0152] The second scheme may be used whether the user terminal 106
knows the neighbor cell's information or not. If the neighbor
cell's information is not available, the user terminal 106 may
search the neighbor cell using the similar scheme used in initial
synchronization described above; however, searching efforts may be
reduced using already known information (i.e., the coarse
synchronization may be omitted because it may be assumed that the
neighbor cell shall use almost the same timing as the serving base
station 104). It may be assumed that there is no integer frequency
offset, because all base stations 104 may use an oscillator as
defined in the standard specification, and after synchronization
with the serving cell this integer frequency offset will likely be
zero. Thus, the preamble sequence identification may be done using
reduced candidates corresponding to no integer frequency offset. In
addition, power calculation and virtual segment detection may be
omitted for the same reason. The serving cell's symbol boundary
position may be excluded from the neighbor cell's symbol boundary
detection process.
[0153] If the neighbor cell's information is available, the
searching and synchronization processes for neighbor cells may be
simplified by using the known information. For example, the coarse
synchronization may be omitted. Also, it may be assumed that there
is zero integer frequency offset. The preamble sequence
identification may be done using the only one known preamble
sequence per corresponding base station 104.
[0154] The synchronization and detection architecture 1100 also
includes a radio frequency (RF) front end 1170, an
analog-to-digital converter (ADC) 1172, a signal buffer 1174, and
an automatic gain control unit 1 176. The output of the ADC 1172
and the output of the CFO/SFO compensation component 1178 are
provided to a multiplexer 1180, which multiplexes these outputs to
the average power determination component 1144, the cyclic
prefix-based auto-correlation component 1128, the conjugate
symmetric-based auto-correlation component 1124, and the reference
cross-correlation component 1126.
[0155] The synchronization and detection methods described herein
may provide fast signal detection, fast preamble detection, fast
searching for the preamble sequence 506 and the segment 510, and
fast integer CFO estimation. For example, with the synchronization
and detection methods described herein, it may be possible to
achieve symbol boundary detection within two symbols (one for
coarse symbol boundary detection, and one for fine symbol boundary
detection). Similarly, using the synchronization and detection
methods described herein it may be possible to detect a preamble
sequence within one frame. This allows real-time processing
capability.
[0156] These results may be achieved with relatively low
complexity. For example, as discussed above, CORRcs (i.e., the
auto-correlation of delivered candidate preamble signal(s) using
the conjugate symmetric (CS) property of the preamble 408) may be
used for purposes of signal and/or preamble detection.
Auto-correlation operations based on the CS property of the
preamble 408 may be less complex than other types of
auto-correlation operations that may be used for signal and/or
preamble detection. As another example, preamble sequence
identification may be performed with respect to a reduced set of
integer CFO candidates. This also may contribute to the reduced
complexity of the methods and apparatus described herein.
[0157] The methods and apparatus described herein may provide
real-time processing capability by reducing computation complexity.
For example, processing may occur within one symbol for coarse
synchronization and fine synchronization, respectively. Processing
may occur within one frame for preamble sequence identification and
integer carrier frequency offset estimation.
[0158] IEEE C802.16e-04/327r1 describes several synchronization and
detection schemes, including a scheme that may be referred to as a
"brute force" search scheme. A comparison will now be made between
the method 900 shown in FIGS. 9 and 9A and the brute force search
scheme described in IEEE C802.16e-04/327r1. Information regarding
the complexity of the brute force search scheme may be found in
IEEE C802.16e-04/327r1.
[0159] Table 1 includes certain information that compares the
method 900 shown in FIGS. 9 and 9A with the brute force search
scheme that is described in IEEE C802.16e-04/327r1. It is assumed
that N.sub.SEQ=284, N.sub.FFT=1024, M=42, N.sub.CP=128, and
N.sub.INT=24. The number of required computations are for a
duration of one frame. The "worst case" refers to the situation
where there is a false detection at the coarse synchronization
stage. Except for the "worst case," it is assumed that there are no
false detections.
TABLE-US-00001 TABLE 1 Comparison of the method shown in FIGS. 9
and 9A with the brute force search scheme that is described in IEEE
C802.16e-04/327r1. Method of FIGS. 9 and Brute force search 9A
(Coarse + Fine) Number of FFTs 48,384 FFTs 3 FFTs or 85 FFTs in the
worst case Number of complex 777,024 265,038 or multipliers (This
number of 286,030 in the multiplications is worst case required per
FFT) Comments on real time Real time processing is All coarse and
fine processing. (Real time almost impossible to synchronization
means that processing implement this scheme processing can be
capability of incoming considering the processed in real signal)
computation complexity time so this scheme can provide fast
searching capability.
[0160] FIG. 12 illustrates various components that may be utilized
in a wireless device 1202. The wireless device 1202 is an example
of a device that may be configured to implement the various methods
described herein. The wireless device 1202 may be a base station
104 or a user terminal 106.
[0161] The wireless device 1202 may include a processor 1204 which
controls operation of the wireless device 1202. The processor 1204
may also be referred to as a central processing unit (CPU). Memory
1206, which may include both read-only memory (ROM) and random
access memory (RAM), provides instructions and data to the
processor 1204. A portion of the memory 1206 may also include
non-volatile random access memory (NVRAM). The processor 1204
typically performs logical and arithmetic operations based on
program instructions stored within the memory 1206. The
instructions in the memory 1206 may be executable to implement the
methods described herein.
[0162] The wireless device 1202 may also include a housing 1208
that may include a transmitter 1210 and a receiver 1212 to allow
transmission and reception of data between the wireless device 1202
and a remote location. The transmitter 1210 and receiver 1212 may
be combined into a transceiver 1214. An antenna 1216 may be
attached to the housing 1208 and electrically coupled to the
transceiver 1214. The wireless device 1202 may also include (not
shown) multiple transmitters, multiple receivers, multiple
transceivers and/or multiple antenna.
[0163] The wireless device 1202 may also include a signal detector
1218 that may be used to detect and quantify the level of signals
received by the transceiver 1214. The signal detector 1218 may
detect such signals as total energy, pilot energy per pseudonoise
(PN) chips, power spectral density, and other signals. The wireless
device 1202 may also include a digital signal processor (DSP) 1220
for use in processing signals.
[0164] The various components of the wireless device 1202 may be
coupled together by a bus system 1222 which may include a power
bus, a control signal bus, and a status signal bus in addition to a
data bus. However, for the sake of clarity, the various busses are
illustrated in FIG. 12 as the bus system 1222.
[0165] As used herein, the term "determining" encompasses a wide
variety of actions. For example, "determining" may include
calculating, computing, processing, deriving, investigating,
looking up (e.g., looking up in a table, a database or another data
structure), ascertaining and the like. Also, "determining" may
include receiving (e.g., receiving information), accessing (e.g.,
accessing data in a memory) and the like. Also, "determining" may
include resolving, selecting, choosing, establishing and the
like.
[0166] Information and signals may be represented using any of a
variety of different technologies and techniques. For example,
data, instructions, commands, information, signals and the like
that may be referenced throughout the above description may be
represented by voltages, currents, electromagnetic waves, magnetic
fields or particles, optical fields or particles or any combination
thereof.
[0167] The various illustrative logical blocks, modules and
circuits described in connection with the present disclosure may be
implemented or performed with a general purpose processor, a
digital signal processor (DSP), an application specific integrated
circuit (ASIC), a field programmable gate array signal (FPGA) or
other programmable logic device, discrete gate or transistor logic,
discrete hardware components or any combination thereof designed to
perform the functions described herein. A general purpose processor
may be a microprocessor, but in the alternative, the processor may
be any commercially available processor, controller,
microcontroller or state machine. A processor may also be
implemented as a combination of computing devices, e.g., a
combination of a DSP and a microprocessor, a plurality of
microprocessors, one or more microprocessors in conjunction with a
DSP core or any other such configuration.
[0168] The steps of a method or algorithm described in connection
with the present disclosure may be embodied directly in hardware,
in a software module executed by a processor or in a combination of
the two. A software module may reside in any form of storage medium
that is known in the art. Some examples of storage media that may
be used include RAM memory, flash memory, ROM memory, EPROM memory,
EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM
and so forth. A software module may comprise a single instruction,
or many instructions, and may be distributed over several different
code segments, among different programs and across multiple storage
media. A storage medium may be coupled to a processor such that the
processor can read information from, and write information to, the
storage medium. In the alternative, the storage medium may be
integral to the processor.
[0169] The methods disclosed herein comprise one or more steps or
actions for achieving the described method. The method steps and/or
actions may be interchanged with one another without departing from
the scope of the claims. In other words, unless a specific order of
steps or actions is specified, the order and/or use of specific
steps and/or actions may be modified without departing from the
scope of the claims.
[0170] The functions described may be implemented in hardware,
software, firmware, or any combination thereof If implemented in
software, the functions may be stored as one or more instructions
on a computer-readable medium. A storage media may be any available
media that can be accessed by a computer. By way of example, and
not limitation, such computer-readable media can comprise RAM, ROM,
EEPROM, CD-ROM or other optical disk storage, magnetic disk storage
or other magnetic storage devices, or any other medium that can be
used to carry or store desired program code in the form of
instructions or data structures and that can be accessed by a
computer. Disk and disc, as used herein, includes compact disc
(CD), laser disc, optical disc, digital versatile disc (DVD),
floppy disk and Blu-ray.RTM. disc where disks usually reproduce
data magnetically, while discs reproduce data optically with
lasers.
[0171] Software or instructions may also be transmitted over a
transmission medium. For example, if the software is transmitted
from a website, server, or other remote source using a coaxial
cable, fiber optic cable, twisted pair, digital subscriber line
(DSL), or wireless technologies such as infrared, radio, and
microwave, then the coaxial cable, fiber optic cable, twisted pair,
DSL, or wireless technologies such as infrared, radio, and
microwave are included in the definition of transmission
medium.
[0172] Further, it should be appreciated that modules and/or other
appropriate means for performing the methods and techniques
described herein, such as those illustrated by FIGS. 9-10, can be
downloaded and/or otherwise obtained by a mobile device and/or base
station as applicable. For example, such a device can be coupled to
a server to facilitate the transfer of means for performing the
methods described herein. Alternatively, various methods described
herein can be provided via a storage means (e.g., random access
memory (RAM), read only memory (ROM), a physical storage medium
such as a compact disc (CD) or floppy disk, etc.), such that a
mobile device and/or base station can obtain the various methods
upon coupling or providing the storage means to the device.
Moreover, any other suitable technique for providing the methods
and techniques described herein to a device can be utilized.
[0173] It is to be understood that the claims are not limited to
the precise configuration and components illustrated above. Various
modifications, changes and variations may be made in the
arrangement, operation and details of the methods and apparatus
described above without departing from the scope of the claims.
* * * * *